Rigid Body Physics Rolling Ball Won't Come to a Stop
Physics engines can be something of a pain, even in commercial packages.  

In your example I tried using two ground-planes, one sloped, the other flat, and it seems no matter what the settings are on the flat plane, the ball appears to all but ignore those that are not extreme. That would make them unusable anyway.



There are two ways to circumvent this.  Substitute the ball with a duplicate which is stripped of physics and animation, or  bake the ball's action from where you want to accelerate it's slowdown.

In both cases, this would occur from one of the bounces after it hits the flat plane.

For expedience I chose to bake the entire action in the gif shown here, but the result would be the same so long as the physics didn't decide to change it's mind at some future date.

When the entire sequence is baked, there's no way the physics engine or changes to it in future Blender versions are going to muck up the project.

Once baked, purge the ball of it's physics and animation. This would probably have to be checked in the Dopesheet also as physics strips have a habit of staying put.  Clear the animation strip in the Outliner.

Once switched to baked keyframes, those beyond the nominated switchover to an accelerated slowdown, can be deleted and substituted with just one other - where it's to stop.  

The Graph Editor's handles can then be adjusted to maintain it's speed initially and also accelerate the slowdown.  You are able to determine exactly where it will stop by dragging the ball there and at the frame where it's to come to a halt. (keyframe it)